Power wrench



Aug. 14, 1934. i MILLER 1,970,179

POWER WRENCH Filed Feb. 10, 1933 ('fiarlesAJlz'ller v W Y f- PatentedAug. 1 4, 1934 UNITED STATES PATENT OFFICE 3 Glaims.

The invention relates to power wrench apparatus and has as an object theprovision of an electrically driven and controlled power wrench fortightening or removing nuts.

It is an object of the invention .to provide a power wrench which may becontrolled to tighten nuts to a predetermined degree of stress upon thebolts.

It is a further object of the invention to provide a power wrench whichwill tighten nuts to a predetermined degree of stress and having meansto vary the degree of this stress in accordance with the size of thebolt for the service required.

It is a further object of the invention to provide an apparatus havingmeans to tighten or remove nuts and means to provide slight motion ofrevolution of the wrench member so as to be applicable to the nut.

It is a further object of the invention to provide a new process oftightening nuts to predetermined degrees of stress.

1 Further objects of the invention will appear from the followingdescription when read in connection with the accompanying drawingshowing an illustrative embodiment of the invention, and wherein: Fig. 1is a plan view;

Fig. 2 is an end view; and

- Fig. 3 is a diagram of circuits.

As shown the device comprises a casing housing an electric motorpreferably of reversible type operated by direct current. To manipulatethe wrench, the casing is shown as J provided with handles 11, 12 whichare preferably hollow for a reason to be described. Sup-- ply wires 13,14 may be contained in a cable leading into the casing preferably at theend thereof as shown. A bearing 15 is shown rigid with the motor casingin which is revolubly mounted a wrench member 16 upon a shaft 17carrying a gear 18 in mesh with a gear 19 upon the motor shaft 20. Thegears 18, 19 are preferably formed so as to provide a reduction of the 1speed at which the wrench may be turned relative to the speed of themotor shaft 20.

.To react against the torque of the wrench applied to a nut, there isshown an adjustable stop member comprising an arm 21 preferably 1 formedin halves having portions 22, 23 that may be clamped upon the bearing 15by means of a bolt 24 to make the arm rigid with the casing. The arm isshown as carrying a projecting member 25 whichalso may be clampedbetween the *halves of the arm 21 as by means of a bolt 26, whereby theprojection of the member 25 from the arm may be varied in accordancewith requirements.

When the wrench 16 is applied to a nut, the projection 25 may bearagainst the structure upon which the nut is being applied so as toprevent rotation of the wrench against the torque applied to the nut.

For control of the motor the electric connections include switches whichmay be of the 655 ordinary push button type and which for convenienceare shown as applied to the arms 11, 12. A switch 27 may be connected toprovide forward movement of the motor in a tightening direction of thenut, a switch 28 for adjustment of the wrench member or to inch themotor, switch 29, which may be utilized to stop the motor when beingused to unscrew nuts, and a switch 30 for reversal of the motor to turnthe same in the direction to remove nuts.

There are also shown diagrammatically in Figure 1 casings carried uponthe motor casing to house relay switches 31, 32, 33, and a casing for anoverload switch 34 having projecting therefrom an ammeter 35 and anadjusting screw The circuits shown in Fig. 3 comprise the' power wires13, 14, the motor being shown diagrammatically at 37. To drive thewrench in the forward or tightening direction, the switch 29 may beclosed providing a circuit through wires 13, 38, switch 29, wire 40,solenoid 33, and wire 42 to wire 14. The core of the solenoid beingdrawn up, the circuit is closed from wire 13 through wire 43, contacts44, wires 45, 46, to brush 47, motor 37, wire 48, overload switch 49,wire 50, contacts 51, wire 52, to wire 14, at the same time providing ahold-up circuit through solenoid 41 by connection thereof to wire bymeans of wire 53. The motor will therefore be revolved in a direction totighten the nut until the load upon the motor due to the tighteningstress reaches the amperage for which the overload switch is set,whereupon this switch will open the circuit to stop the motor and toallow the core of solenoid 41 to fall back, thereby breaking thecircuits at contacts 44, 51.

' If the wrench member is not in proper, position of revolution forapplication to the nut, closure of switch 30 will close the contacts 54,55, close a shunt about the switch 29 and through the motor from wire 46through switch 30, contacts 54, and wire 56 to wire 13 and through wire50, contacts 55, Wire 57 to wire 14, thus causing the motor to operatewhile the switch is held closed.

In the application 0! the invention to tightening fish plate bolts upona railway, I have found that a two-horse power motor is sumcient andthat the current to such a motor for the purpose of this inching may becontrolled by a simple push button type of switch.

To revolve the motor in a direction to unscrew nuts, automatic stoppingof the motor is of no interest. The circuit shown for producing thisdirection of revolution of the motor comprises for starting the motor,wire 58, switch 27, solenoid 59, and wire 60 to wire 14. The core ofsolenoid 59 being drawn up closes a circuit from wire 13 through wire61, contacts 62, wire 48, motor 37, wire 46, contacts 63, wire 64, towire 14. When contacts 63 are closed, a holdup circuit is applied tosolenoid 59 by connection or the solenoid to one of the contacts 62 bywire 65.

To stop the motor when the nut has been completely removed, switch 28may be closed providing a circuit from wire 13 through wire 66, switch28, solenoid B'l, wire 68, to wire 14, drawing the core of solenoid 67up and opening the circuit through wire l by operation of contacts 69.

The amperage at which the overload switch 49 will open may be set byadjustment of spring 70 by means of a set screw 36.

While I have shown the relays and the overload switch carried upon themotor casing in Figure 1 for the purpose of providing a selfcontainedtool that may be operated as readily as an electric drill, yet it willbe understood that the relay switches and the overload switch may bemounted upon a switchboard at a position remote from the wrench itselfand this arrangement has been applied and found convenient in theconstruction of a fish plate bolt tightening arrangement for use uponrailways.

When the wrench is to be used for removing a nut, initial loosening ofthe nut by means of the motor would apply a severe load to the motor. Toenable the nut to be initially loosened by power oi the user applied tothe handles 11, 12, I have indicated a dog '71 carried upon the gearcasing and having an end which may be pressed into engagement with oneof the gear teeth of gear 18. The dog 71 is shown as held normally outof engagement with the gear teeth by means of spring '72. To loosen anut, the dog may be pressed into contact with the gear and strainapplied to the handles which will hold the dog into contact until thenut is loosened whereupon the switch 27 may be closed and the gearstarted into revolution, which revolution by cam action against thesurface 73 of the dog will throw the same out of the path of movement ofthe gear teeth where it will be held by the spring 72. K

It will be noted that by the use of hollow handles 11 and 12, the wiresto the push buttons carried by the handles may be located inside thehandles so as to have all the circui enclosed and protected.

I am aware that power wrenches have been constructed which transmitpower from the power means to the wrench element by means of frictionclutches, the slipping of the clutch when the nut has been tightened tothe desired degree being depended upon for preventing overtlghtening ofthe nut. Such deviceshave the defect that the slippage of the clutch isa very variable matter, depending upon the condition of the frictionsurfaces and is modified by wear, atmospheric conditions and many otherelements which render that type of device unsatislactory in use. By thepresent invention, such inaccuracy and irregular results are entirelyobviated.

It is found that with a two-horse power motor geared for reduction ofsubstantially twenty to one, and with the overload switch set at 25amperes, a stress oi. substantially thirty-six thousand pounds isproduced upon the nuts ordinarily used upon fish plates upon railways.By the use of the same motor with the overload switch set as low as oneto five amperes, much smaller nuts may be turned to an adjusted stresswhich is fitted to the service required and it is further found that theresults are substantially uniform throughout the nuts tightened with thesame device set at the same amperage for throwout of the switch.

Obviously the shaft 1"! may be equipped with means for the applicationof socket wrenches corresponding to 16 of a variety oi" sizes readilyremovable and interchangeable. Such structure forming no part of thepresent invention is not illustrated herein.

The operation of the device will be clear from the above description.Minor changes may be made in the physical embodiment the inventionwithin the scope of the appended claims without departing from thespirit thereof.

I claim:

3.. Wrench apparatus comprising, in combination: a frame; handlescarried by said irame; a reversible electric motor and a rotatablewrench geared to be driven by said motor; said wrench, gearing, andmotor carried by said frame; circuit connections :ior forward drive,reverse drive, jogging drive of said motor and for stopping reversedrive thereof; and switches for controlling each of said circuitconnections carried by said handles within reach of an operator graspingsaid handles.

2. Wrench apparatus comprising, in combination: a frame comprising acasing; handles projecting in opposite directions from said casing: areversible electric motor and gearing driven thereby housed in saidcasing; a wrench journaled in said casing to be rotated by said gearing;solenoid operated switches for controlling forward drive, reverse driveand for stopping reverse drive oi? said motor and an overload switch forstopping forward drive of said motor, carried by said casing; pushbutton switches to control said forward, reverse and stopping switchesrespectively and for jogging said motor carried by said handles to beunder the hands oi an operator grasping the same.

3. Wrench apparatus comprising, in combination: a frame comprising acasing; a motor and a rotatable wrench driven thereby carried by saidcasing; a stop arm clamped upon said frame for adjustmentcircumferentially of said wrench; a stop pin clamped to said armprojecting substantially parallel with the axis of said wrench andadjustable as to the extent of its projection from said arm.

CHARLES A. MILLER.

